Overview of the ARPANET

Learn about the first public packet-switched computer network: the ARPANET.


Before there was the internet, there was the ARPANET. The ARPANET was founded by the Advanced Research Projects Agency (ARPA) of the United States Department of Defense as a prototype of a packet-switched network for connecting computer resources. It would be developed into a coherent computer network and later subsumed into the larger global internetwork—the internet.

First connection

The first connection between a pair of ARPANET hosts was made in October 1969, just following the moon landing in July that same year (with the Woodstock music festival sandwiched somewhere in between). A four-host network appeared in December 1969, and the network was progressively scaled up through the ’70s and ’80s and was finally decommissioned in 1990. This was where the Internet protocol suite and the TCP/IPTransmission Control Protocol/Internet Protocol set of protocols were first born and trialed.

The growth of the fledgling network was described in a series of ARPANET logical maps, which make for compelling reading. These show the nascent network as graphs of (network) nodes and (computer) hosts with lines connecting them, which get progressively more complex. A published example of network topology for December 1972 is given in RFC-432 (Network logical map).

December 1970 network

The figure here shows the state of the network in December 1970, with 13 nodes (in blue) and 21 hosts (in white), and 40 edges between them. (There are also two user hosts not shown, which are connected via the server hosts.)

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